The present invention relates to braking system for vehicles with multiple trailers, and in particular to a system and method for determining the operational status on an anti-lock braking system in a chain of multiple-trailers being towed by a commercial vehicle.
Commercial vehicles such as Class 8 tractor-trailers are more frequently being configured with the tractor towing more than one trailer. Typically, the hitch pin of a first trailer is received by the tractor, and fifth-wheel dolly units connect the following trailers to one another, i.e., a fifth-wheel dolly unit attached to the rear of each leading trailer receives the hitch pin of a following trailer.
With each additional trailer unit in the tractor-trailer combination, the vehicle dynamics become more complicated, making it more difficult for the tractor operator to maintain full control over the movements of the multiple trailers. Maintaining control of the entire vehicle train is of particular concern during braking events, when any of several factors (such as misalignment of one or more of the trailers in the train, different surface conditions under different trailer and dolly wheels, different braking forces generated at the individual trailer and dolly wheel brakes, and/or braking system defects in individual trailers) can lead to unstable braking and undesired lateral trailer motion. These undesired motions may not only disturb one trailer's response to the braking event, they may also propagate to the other trailers, increasing the chances for trailer jack-knifing, overturning, and/or collision with adjacent vehicles and/or road-side objects.
It is well known in the art to equip commercial vehicles with antilock braking (“ABS”) systems and stability control systems to improve vehicle stability by minimizing wheel locking and undesired yawing motions (for example, by unlocking individual wheels or the wheels of individual axles, or selectively applying wheel brakes on one side of the vehicle to reduce lateral motion relative to the vehicle travel direction). While such systems have been successfully applied to commercial vehicles having a single trailer in direct electrical, pneumatic and/or hydraulic connection with the tractor's braking and stability control systems, automated trailer braking on commercial vehicle combinations with multiple trailers is less common, in part because integration of anti-lock braking and/or stability control systems in multiple trailer vehicles depends on all of the trailers being equipped with ABS systems, all of the trailers' ABS systems being functional when the vehicle is being operated, and all of the trailers' systems communicating their status to the tractor.
Detection of the number of trailers and dollies in multi-trailer commercial vehicles is not a current industry practice, and state-of-the-art systems in North America do not reliably evaluate the presence and status of trailer ABS systems on multiple trailers. Thus, automated trailer braking is limited, with current automated braking systems typically not applying braking using the full available braking pressure to trailers (i.e., limiting the automated trailer brake pressure and pulse the brakes to minimize lateral instability as best as possible in the circumstances) if it is not known whether one or more of the trailers and/or dollies in the combination is not ABS-equipped, or whether one or more of the trailers has a non-functioning ABS system.
The present invention addresses these and other problems in an efficient and cost-effective manner, without requiring every trailer in a multi-trailer vehicle train to be equipped with additional components or to conform to a particular configuration specification. Rather, in the present invention the braking status of the trailers and dollies in a multi-trailer train is determined by automatic measurement and calculation.
As part of the approach of the present invention, a processor on the vehicle, such as an ABS system controller or a separate controller, determines the total vehicle mass based on the dynamic response of the vehicle to an input. For example, the amount of output torque of the engine and the vehicle's acceleration response to the applied output torque may be used to derive an estimate of the vehicle mass. Separate from the total vehicle mass estimate based on dynamic response, the total load of the vehicle may be estimated by summing the vehicle loads (e.g., the tractor's load on its wheels including the load from the first trailer attached to the tractor, plus the loads on the trailer axles and the dollies reporting to the tractor). These mass and load estimates are then subjected to a plausibility analysis to determine whether all of the trailers and dollies are communicating with the vehicle controller, and thus whether all of the trailer and dolly braking systems (including their respective anti-lock braking and stability control systems) are available to support full application of the vehicle brakes during subsequent braking events.
Once the ABS and/or stability control system status of the vehicle train is known, if any of the trailers or dollies are determined to not have properly reported their data to the vehicle controller, the controller may then operate the brakes in a subsequent braking event at a reduced level intended to avoid brake application at a level high enough to induce wheel skidding (i.e., wheel behavior that would otherwise be ameliorated by an active ABS and/or stability control system).
Alternatively, if the vehicle is equipped for individual trailer and dolly braking system control, the vehicle's ABS and/or stability control systems may be adapted to recognize the actual present braking capabilities of the each of tractor, trailers and dollies, and thereby prepare the system to apply the tractor, trailer and dolly brakes on an individual brake and/or individual axle basis in a manner that takes into account the determined variations in braking capacity. Accordingly, the present invention provides the ability to increase the available braking force that may be applied to the vehicle, as compared to the prior art default operating state if the braking status of the trailers and dollies was unknown, i.e., limiting brake application at the trailers and/or dollies to avoid over-braking and resulting vehicle instability. The present invention thus provides the ability to improve the overall vehicle train braking performance and stability by tailoring the brake application to the specific vehicle configuration.
The loads on each of the tractor, dollies and trailers may be measured or otherwise determined in a variety of ways. For example, on vehicles equipped with air suspensions, the loads may be measured using pressure sensors. If the vehicles have mechanical suspensions without load detection sensors (e.g., leaf spring suspension), the load may be measured using ride height sensors. An optical detection system could also be used to detect the number of trailers and dollies in the vehicle train, either by an optical system hosted on the vehicle or by an optical system that is part of yard infrastructure that transmits data to the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.